The music created by a grand piano has a classical and refined sound. Most commonly a musical performance of a pianist is recorded using microphones and played back using speakers. In most cases, the recorded musical performance loses its dramatic and cathartic effect and the essence of the grand piano is lost.
A fuller sound is created by a piano when compared to that produced by a speaker system. There is a growing trend for people to prefer to listen to a piano played in real-time rather than listen to a recorded version of the same performance played through speakers. However, playing, or employing a pianist to play a piano whenever there is a need for music is not often practical, desirable or economical. Automatic pianos provide a solution to this problem.
Automatic pianos are configured to recreate a musical performance from a log of instructions recording how the piano was played and manipulated during the original musical performance. In this way, automatic pianos allow the listener to experience the same or similar quality of sound output produced when the musical performance was originally played. In addition, quality automatic piano systems which use a high quality recording of how a piano was played can give a listener the feeling that they are in the presence of the recording pianist and are experiencing each nuance and fine detail of the musical performance first-hand.
Some conventional recording systems for automatic pianos employ a simple and cheap method of attempting to capture the musical performance of a pianist by measuring the motion of the piano key as it is played. However, the motion of the keys and the movement of the hammer are connected by a very complex and chaotic relationship, which leads to a recording based on the motion of the keys producing very unmusical reproductions when played back on an automatic piano.
Recording the musical performance of a pianist on a piano by using the velocities of the hammers as they move, as a measure of both the loudness and strike-time of a note, provides a more accurate representation not just of the piece of music itself, but also the flair and unique style of the pianist.
One of the major difficulties in attempting to measure the hammer velocity is the constraint of finding an accessible location for the measurement hardware, without involving invasive engineering to the structure and mechanism of the piano. As such, conventional systems that measure the velocity of the hammers of a piano can be very invasive and destructive to the piano, and are irreversible. For example, U.S. Pat. No. 4,307,648 (STAHNKE) discloses a method of using notched shutters inserted into a machined longitudinal slot on each hammer. The notched shutters interrupt an optical switch resulting in an electronic counter being turned on when top edge of the shutter intercepts the optical switch and being turned off when the bottom edge of the notch intercepts the optical switch. The velocity of the hammer is determined from the time counted between the electronic counter being turned on and then off.
As disclosed in the description of U.S. Pat. No. 4,307,648 (STAHNKE), the method necessitates making room for the optical switch assemblies to work with the optical shutters. Additional modifications include thinning of the wrest plank of the piano, reduction of the length of the tuning pins and, often, machining the underside of each wooden key to remove a quantity of wood to make room for additional key-sensor optics. The dual task of simultaneously skimming wood and steel presents serious machining problems and further to this, due to the machining, the keyboard lid is repositioned and often does not close properly over the keys. Additionally, the fitting of the notched shutters to the hammers requires each hammer to be removed and clamped in a jig so that a very fine slit (0.254 mm or one ten-thousandth of an inch) and a 1.5 mm hole can be machined to fasten the notched shutter or “flag”. The hammers then need to be re-inserted into the piano which results in a time consuming task of realigning the hammers in the piano, this often leads to the hammers not being aligned correctly which negatively effects the music produced by the piano. As a consequence of removing wood from the piano keys the whole piano action is then wrongly weighted which requires extra weights to be measured and added to each key. Modifications of this kind are largely irreversible and cause a piano to lose at least some of its original integrity.
A further example of recording hammer velocities is given in U.S. Pat. No. 5,627,333 (STAHNKE) which moves away from the idea of using hammer flags or shutters and instead discloses calculating the time between a hammer assembly intersecting a first and a second optical beam from first and second photo-interrupters, respectively, and then determining the hammer velocity from the calculated time.
U.S. Pat. No. 5,627,333 (STAHNKE) also discloses a method for correcting the position of the second photo-interrupter post-installation as the second photo-interrupter can deviate from its correct position and cause a recording log to be different to the original performance that was played. The post-installation method involves calculating a correct distance from the impact point of each hammer on each respective string at which to place each second photo-interrupter, and displaying the correct distances for each key on a screen for a user to tune each respective second photo-interrupter. The need to perform a post-installation correction to the system of U.S. Pat. No. 5,627,333 (STAHNKE) in this way is an indication that using first and second photo-interrupters is a method that is not consistently accurate over time and with changing environmental conditions. Also this method is very time consuming and difficult to perform accurately, with emphasis on the correct mechanical alignment and measurement of multiple components.
U.S. Pat. No. 5,194,685 (KAWAMURA et al.) also moves away from using hammer flags and discloses reflecting light from a hammer to determine the velocity of the hammer and claims to provide a system that is not very invasive with reduced production steps. U.S. Pat. No. 5,194,685 (KAWAMURA et al.) uses the strength of a reflected light signal to determine the distance of the hammer from the sensor. Differentiation is then used to determine firstly the velocity and secondly the acceleration of the hammer at incremental differences in position which involves considerable computational processing. Further to this, U.S. Pat. No. 5,194,685 (KAWAMURA et al.) performs unspecified weak, medium and strong strength test strikings and stores digital signals associated with each test strike as standards in a correction table. The table is then used to categorise future strikings as one of weak, medium or strong strength strikings and the value of velocity calculated is corrected according to this table resulting in the calculated velocities being generalised into velocities that do not correctly represent the original performance of the pianist on the piano. U.S. Pat. No. 5,194,685 (KAWAMURA et al.) has not been commercially implemented in the 21 years since the publication of U.S. Pat. No. 5,194,685 (KAWAMURA et al.) in 1993.
It is advantageous that when recording the musical performance of a pianist for playback on an automatic piano, it is known which key of the keyboard has been pressed to determine at least when a string damper of the piano is in contact with its respective string. Both U.S. Pat. No. 5,627,333 (STAHNKE) and U.S. Pat. No. 5,194,685 (KAWAMURA et al.) use key sensors to do this, however both of these methods require sensors to be installed beneath each key of the keyboard which can be a time consuming task that requires the underside of each key to be slimmed down and which will result in the keys needing to be corrected so they are not off balanced, as mentioned above.
It is important that, when moving away from the use of hammer flags by instead implementing optical sensors, as in U.S. Pat. No. 5,194,685 (KAWAMURA et al.), the light-sensitive optical systems are shielded from daylight and artificial tungsten light during use, and also during calibration. Typically when the keyboard and optics are returned to their proper place in the keyboard instrument they are largely shielded from ambient light. If, however, bright studio lights are used to illuminate the piano, special precautions may be necessary.
Thus, it is an objective of the invention to provide a hammer velocity measurement system that can be successfully implemented using non-invasive and non-destructive procedures to fit the system to a keyboard instrument. A further objective of the invention is to provide a system that once removed from a keyboard instrument does not render the keyboard instrument defunct, or at least preserves more of the integrity of the keyboard instrument than prior art systems. A further objective of the invention is to provide a more precise and accurate representation of how the keyboard was manipulated by a pianist. A further objective of the invention is to provide a hammer velocity measurement system that is easier and quicker to set up and calibrate. A further objective of the invention is to provide a way of identifying when each key is pressed in an accurate and non-invasive way.